Apparatus for ventilating the crankcase of a combustion engine

ABSTRACT

The invention relates to a device for crankcase ventilation of an internal combustion engine, comprising a ventilation duct extending from the crankcase to an induction tract of the internal combustion engine, whereby at least one oil vapor separator causing a drop in pressure is arranged in said duct and a crankcase vacuum control valve is arranged upstream or downstream therefrom and can be adjusted according to the pressure in the crankcase such that a lower pressure threshold valve in the crankcase is respected. The novel device is characterized in that a discharge duct extending from the crankcase to the induction tract of the internal combustion engine is also provided, whereby a crankcase overpressure limiting valve is disposed inside said duct and can be adjusted in a pressure-dependent manner to ensure that an upper pressure threshold in the crankcase is not exceeded.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for ventilating thecrankcase of a combustion engine, comprising a ventilation duct runningfrom the crankcase to an intake section of the combustion engine and atleast one oil-mist separator that causes a pressure drop and is arrangedin the course of the ventilation duct, with a crankcase vacuum pressureregulating valve that is installed upstream or downstream of theoil-mist separator and is adjustable dependent on the crankcase pressuresuch that the pressure in the crankcase is prevented from falling belowa lower pressure limit value.

During operation of a combustion engine, gas is pressed out of thecombustion chamber and into the crankcase through the gap between thepiston rings and the cylinder walls, this gas being called blow-by gas.This gas increases the pressure in the crankcase and must, therefore, beremoved. Usually, the blow-by gas is supplied into the intake section ofthe combustion engine via a crankcase vacuum pressure regulating valve.Emission of noxious substances out of the crankcase is, thus, avoided.The regulating valve is provided to maintain a range of pressure in thecrankcase that is optimal from a technical point of view. Too low acrankcase pressure must be avoided in order to prevent foreignsubstances from entering into the crankcase from outside through leaks.Too high a crankcase pressure must, vice versa, also be avoided in orderto prevent oil or gas from exiting through leaks in an uncontrolledmanner.

The blow-by gas contains fine oil particles in the form of oil mistwhich might cause malfunctions of the combustion engine when the gas isbeing returned into the intake section of the combustion engine. Forthat reason, the oil mist must be separated from the gas. To achievethis, at least one separator is arranged in the course of theventilation duct carrying the blow-by gases, usually either as acoalescer made of textile fiber materials or as a cyclone. An apparatusfor ventilating the crankcase of a combustion engine comprising thefeatures and functions illustrated above is described in the applicant'snon-prepublished German utility model registration application 200 09605.2.

The performance of the separator in such an apparatus is, in particular,determined by the flow resistance that is generated by the respectiveblow-by gas volume flow. In this context, it can generally be observedthat a high separation rate is associated with a high flow resistanceand vice versa. The flow resistance in the separator is a disadvantagein that it also increases the pressure in the crankcase accordingly. Ifthe combustion engine is, for example, in operating states where it issubject to high speeds and high load, this increase in pressure in thecrankcase is compensated by the high vacuum pressure that is thenpresent in the intake section. In this manner, the pressure in thecrankcase is prevented from assuming too high values. If, however, thevacuum pressure in the intake section of the combustion engine is onlylow, as is the case at low speeds or in the deceleration mode of thecombustion engine, then there is the risk of the pressure in thecrankcase rising to an impermissibly high value.

SUMMARY OF THE INVENTION

For that reason, the present invention aims at creating an apparatus ofthe aforementioned type, which obviates the drawback disclosed andwhich, in particular, ensures that the pressure in the crankcase isreliably prevented from assuming values that are too low or too high andwhich, at the same time, ensures that the oil mist is, all in all,separated from the blow-by gas in a satisfactory manner.

This problem is solved by the invention by an apparatus of theaforementioned type, characterized in that a relief duct is, inaddition, provided, said relief duct running from the crankcase to theintake section of the combustion engine, wherein a crankcase excesspressure limiting valve is arranged in the course of said relief duct,which valve can be adjusted dependent on the pressure such that an upperpressure limit value is prevented from being exceeded in the crankcase.

The additional relief duct and the crankcase excess pressure limitingvalve provided therein are advantageous in that too high a pressure isprevented from developing in the crankcase in any operating state of thecombustion engine. Once the pressure in the crankcase reaches a maximumlimit value, the limiting valve and, thus, the relief duct is opened,limiting the pressure in the crankcase to this specifiable maximumpressure limit value. During operation of the combustion engine, theblow-by gas does not only flow through the relief duct, even if thelimiting valve is open; a part of the blow-by gas also flows through theventilation duct and the oil-mist separator provided therein. If thepressure in the crankcase is below the upper pressure limit value, thelimiting valve is closed and blow-by gas does not flow through therelief duct. In this case, the total amount of blow-by gas flows throughthe ventilation duct and the oil-mist separator provided therein. Hence,the relief duct is opened only in operating states of the combustionengine that occur relatively rarely. The relief duct is closed by theexcess pressure limiting valve for most of the operating time. In orderto achieve quick and efficient relief from pressure in the crankcase ifneed be, components with an excessively high flow resistance which mightcause development of a differential pressure are not provided in therelief duct. If necessary, it may be appropriate to incorporate anadditional coarse-particle separator with low resistance in the reliefduct, in order to also avoid oil from being entrained over to the pureor oil free side when the relief duct is open. Hence, it must also beassumed that the oil mist contained in the blow-by gas flowing throughthe relief duct is not completely separated therefrom. This appears tobe to disadvantage at first sight, but does, in practice, notdeteriorate the effect of the apparatus as such.

Totaled over all operating ranges during normal operation of thecombustion engine, the apparatus according to the invention, as such,results in a better oil-mist separation than the apparatuses used sofar, because the number of operating points where the relief duct isopen is relatively low as compared with the number of operating stateswhere the relief duct is closed.

Alternatively, the relief duct provided according to the inventionprovides the advantageous possibility of designing the oil-mistseparator arranged in the ventilation duct with a higher efficiencysince a higher pressure drop over the oil-mist separator no longerresults in problems to the combustion engine, caused by too high apressure in the crankcase.

It is, furthermore, possible to design the geometry of the relief ductand the crankcase excess pressure limiting valve arranged therein suchthat, by appropriately routing and diverting the flow, there will be animpingement separation of oil droplets without there being a pressuredrop, so that the oil mist and, in particular, any coarse-particle oilis, at least in part, also separated from the blow-by gas in the reliefduct. This also prevents coarse-particle oil from being entrainedthrough the relief duct.

It is, furthermore, preferably provided that the crankcase excesspressure limiting valve can be adjusted dependent on the differencebetween the crankcase pressure and a reference pressure. In this manner,a particularly exact pressure limit value can be specified for thepressure in the crankcase.

It is appropriate to use the atmospheric pressure directly as thereference pressure for the crankcase excess pressure limiting valvebecause this pressure can be considered to be the upper pressure limitvalue for the crankcase pressure. Thus, a technically simple solution isto allow a pressure in the crankcase that is negative as compared withthe atmosphere. The fact that the atmospheric pressure is available atall times and in all places is to further advantage. It is, however,also possible to select any vacuum source desired as reference pressure.

Furthermore, the crankcase excess pressure limiting valve is preferablya diaphragm valve with a diaphragm. On the one hand, this reliablyensures proper functioning and, on the other hand, precise responding ofthe valve, because the differences in pressure that occur are onlyrelatively small.

In a preferred embodiment of the diaphragm valve, the diaphragm is fixedin a diaphragm chamber inside the crankcase excess pressure limitingvalve and subdivides said diaphragm chamber into a first chamber sectionthat is connected to the atmosphere and a second chamber section that isconnected to the crankcase. Pressures which are governing the valveposition are, thus, applied to the diaphragm directly and without anymechanical intermediate elements.

Furthermore, it is preferably provided that a beginning of that part ofthe relief duct that is running to the intake section is positioned inthe crankcase excess pressure limiting valve, wherein said beginning isformed as a valve seat that is directly cooperating with the diaphragmserving as a part of the valve body and is arranged in the secondchamber section. This permits, advantageously, to achieve a limitingvalve, the only moving part of which is the diaphragm, thus providing astructure that is as simple as possible from a mechanical point of view.A valve spring can be provided as an option. A separate valve body isnot required either since the diaphragm itself acts as a valve bodydirectly cooperating with the valve seat. As long as the pressure in thecrankcase is below the atmospheric pressure, the atmospheric pressureensures that the diaphragm is supported by the valve seat so that thevalve then assumes its closing position and shuts off the relief duct.The vacuum pressure present in the intake section additionally ensuresthat the diaphragm is tightly resting on the valve seat, since thevacuum pressure in the intake section propagates without any pressureloss through the part of the relief duct the beginning of whichrepresents the valve seat. Only if the pressure in the crankcase risesto a value above the atmospheric pressure will the diaphragm be liftedoff the valve seat and the relief duct be opened.

To ensure that the diaphragm is reliably lifted off its valve seat asdescribed above, it is appropriately provided that the effective area ofthe diaphragm is a multiple of the cross-sectional area of the valveseat. In this manner, the effect of the vacuum pressure in the intakesection on the adjustment of the diaphragm is minimized so thatadjustment of the diaphragm is, in essence, determined only by thepressure ratio between the crankcase and the atmosphere.

A further embodiment of the apparatus provides that an additional ductbypassing the oil-mist separator is provided, said bypass duct runningfrom the inflow side to the outflow side of the oil-mist separator, witha bypass valve, a so-called separator differential pressure limitingvalve, being arranged in the course of said bypass duct. Said separatordifferential pressure limiting valve can be manufactured such that,depending on the difference between the inflow-side pressure on thedirty side of the separator and the outflow-side pressure on the cleanside of the separator, it is adjustable such that it opens if aspecifiable maximum pressure difference over the oil-mist separator isexceeded. This bypass duct, including its separator differentialpressure limiting valve, ensures that blow-by gas flows around theoil-mist separator if there is an excessive pressure drop over theoil-mist separator, for example because the latter is clogged by oil, sothat, in this case, additionally positive crankcase pressures areavoided which might, otherwise, develop as a result of an overload ofthe relief duct. Moreover, it is, hence, possible to design the reliefduct with a relatively small cross-section, thus saving free space. Thebypass valve can also be used to provide the operating personnel of thecombustion engine with a device indicating that the oil-mist separatorrequires maintenance, for example replacement of a separator insert.

To minimize the number of line connections and other connections duringassembly of the apparatus and its attachment to a combustion engine, itis, advantageously, provided that the ventilation duct and the reliefduct are designed as a common duct section over a part of their lengthupstream and/or downstream of the oil-mist separator and of theassociated crankcase vacuum pressure regulating valve.

Over and above this, it is furthermore provided that, in order toachieve a compact construction and an easy connectability of theapparatus to an associated combustion engine, the oil-mist separator,the crankcase vacuum pressure regulating valve, the separatordifferential pressure limiting valve and, if provided, the crankcaseexcess pressure limiting valve as well as at least partial sections ofthe ducts are comprised to form one assembly-forming module that can beconnected to the associated combustion engine either directly or viatubings or pipelines.

BRIEF DESCRIPTION OF THE DRAWING

An exclusive example of the invention will be illustrated below by meansof a drawing, in which:

FIG. 1 is a schematic functional representation of an apparatus forventilating the crankcase of a combustion engine; and

FIG. 2 is also a schematic representation of a crankcase pressurelimiting valve as a part of the apparatus according to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To its extreme right, FIG. 1 of the drawing shows a combustion engine 2that comprises a crankcase 21 in its lower part and one or morecombustion chambers 23 in its upper part. An intake section 22 throughwhich combustion air is supplied to the combustion chambers 23 of thecombustion engine 2 ends in the combustion chambers 23.

An apparatus 1 for ventilating the crankcase 21 is allocated to thecombustion engine 2. This apparatus 1 first comprises a ventilation duct10 that starts in the crankcase 21 and extends to the intake section 22.An oil-mist separator 11 used to separate oil mist consisting of fineoil droplets from blow-by gas that is supplied from the crankcase 21into the intake section 22 is arranged in the course of this ventilationduct 10. Furthermore, a crankcase vacuum pressure regulating valve 12 isprovided in the ventilation duct 10, downstream of the oil-mistseparator 11 as seen in flow direction. This regulating valve 12 servesto limit the vacuum pressure in the crankcase 21 that is caused by thevacuum pressure present in the intake section 22 to a specifiable vacuumpressure value; for technical reasons, the pressure in the crankcase 21must not fall below this specifiable vacuum pressure value.

Furthermore, the apparatus 1 comprises an oil-separator bypass duct 13that branches off the ventilation duct 10 upstream of the oil-mistseparator 11 and that ends in the ventilation duct 10 downstream of theoil-mist separator 11. A separator differential pressure limiting valve14 that is adjustable subject to the pressure drop over the oil-mistseparator 11 is arranged in the course of this bypass duct 13. Once thepressure drop over the oil-mist separator 11 exceeds a specifiable upperlimit value, the bypass valve 14 opens so that at least a part of theblow-by gas bypasses the oil-mist separator 11 and flows through thebypass duct 13. A line/return 16 of separated oil from all regions ofthe separator system back into the oil pan 26 of the motor 2 is providedat the bottommost point of the system. In order to avoid any undesiredgas flow extending from bottom to top through the oil return duct 16, itis provided to design the lower end of the duct 16 such that itcomprises a siphon or a check valve.

Up to this point in the description, the apparatus 1 corresponds tocurrent apparatuses for the ventilation of crankcases.

The essential innovation of the apparatus 1 illustrated in FIG. 1comprises provision of an additional relief duct 15 that connects thecrankcase 21 to the intake section 22. The only component incorporatedin this relief duct 15 is a crankcase excess pressure limiting valve 3that ensures that any harmful excess pressure in the crankcase 21 isavoided. The limiting valve 3 is designed such that it opens the reliefduct 15 as soon as the pressure in the crankcase 21 exceeds theatmospheric pressure. Any excess pressure in the crankcase 21 is, thus,relieved quickly and efficiently or is avoided from the start. Afine-particle oil-mist separator or any other component causing anexcessive and, thus, disturbing pressure drop is not provided in thecourse of the relief duct 15, so that, when the limiting valve 3 isopen, the pressure in the crankcase 21 immediately drops to the pressurepresent in the intake section 22. Since, compared with the atmosphericpressure, a certain, though low vacuum pressure is still present in theintake section 22 even in case of the most unfavorable operating statesof the combustion engine, a pressure in excess of the atmosphericpressure is, at any rate, avoided in the crankcase 21.

Since an oil-mist separator is not arranged in the relief duct 15, thereis no selective and complete fine-particle oil-mist separation; byappropriately routing and forming the relief duct 15, however, it ispossible to achieve partial separation of coarse-particle oil/oilsplashes by a part of the oil droplets being separated by means ofimpingement separation and being collected on the walls of the reliefduct 15. From there, selective drainage, for example into a collectiontank or into the crankcase 21 of the combustion engine 2, can beachieved in the same manner as is known from the usual oil-mistseparators.

In the apparatus according to FIG. 1, the oil-mist separator 11 can bedesigned with a high degree of separation, resulting in a highdifferential pressure. Here, however, this high differential pressure isnot harmful to the pressure in the crankcase 21, since the crankcasepressure is, with priority, limited upwards by the crankcase pressurelimiting valve 3 that is separately provided in the relief duct 15. Allin all and over the various operating states and the life of thecombustion engine 2, the apparatus 1, thus, provides a degree ofseparation of oil droplets from the oil mist that is, altogether, higherthan that of usual apparatuses which are not provided with a relief duct15 comprising a crankcase excess pressure limiting valve 3.

FIG. 2 of the drawing shows a possible embodiment of the crankcaseexcess pressure limiting valve 3 as part of the apparatus 1 from FIG. 1.A section of the part of the relief duct 15 coming from the crankcase21, which ends in a diaphragm chamber 30 of the limiting valve 3 throughan inlet 33, can be seen to the lower left of FIG. 2. A diaphragm 35that is movable in perpendicular direction to its area plane andsubdivides the diaphragm chamber 30 into an upper chamber section 31 anda lower chamber section 32 is fixed in the diaphragm chamber 30. Theupper chamber section 31 is connected to the open atmosphere via a hole31′ so that the pressure present in the upper chamber section 31 alwayscorresponds to the atmospheric pressure.

The inlet 33 ends in the lower chamber section 32. Furthermore, thebeginning of the second part of the relief duct 15 running from thelimiting valve 3 to the intake section 22, which forms an outlet 37 ofthe limiting valve 3, is arranged in the lower chamber section 32 of thediaphragm chamber 30. The beginning of this section of the relief duct15 is arranged concentrically to and underneath the diaphragm 35 andforms a valve seat 34. The diaphragm 35 which here, at the same time,acts as valve body cooperates with this valve seat 34.

As long as the pressure in the crankcase 21 to which the relief duct 15is connected on the side of the inlet 33 of the limiting valve 3 isbelow the atmospheric pressure, the atmospheric pressure presses thediaphragm 35 onto the valve seat 34, so that the limiting valve 3 and,thus, the relief duct 15 is then closed. Once a pressure that exceedsthe atmospheric pressure develops in the crankcase 21, the difference inpressure on the two sides of the diaphragm 35 causes said diaphragm tobe lifted off the valve seat 34, so that the limiting valve 3 and therelief duct 15 are now open. In this condition, blow-by gas starts toflow through the relief duct 15 from the crankcase 21 and directly intothe intake section 22, as represented by the arrows in FIG. 2. Once thepressure in the crankcase 21 has again dropped to a value below theatmospheric pressure, the diaphragm 35 returns to its closed position,thus closing the relief duct 15.

If the valve 3 is to open and close at other pressure values, anadditional compression spring 36 exerting on the diaphragm 35 apreloading force that acts in opening direction can be arrangedunderneath the diaphragm 35, as indicated in FIG. 2.

As is illustrated by FIG. 2, the blow-by gas is subjected to a sharpredirection within the range of the valve seat 34, when the crankcaseexcess pressure limiting valve 3 is open. This redirection causes atleast a part of the oil droplets that are carried along in the blow-bygas to deposit on the underside of the diaphragm 35 as a result ofimpingement separation and to drip from there into the lower section ofthe diaphragm chamber 30. From there, the oil can be drainedselectively, this process not being shown here. In this manner, at leasta part of the oil mist is separated from the blow-by gas flowing throughthe relief duct 15, even if a special oil-mist separator is not arrangedin the course of the relief duct 15.

As is apparent from the foregoing specification, the invention issusceptible of being embodied with various alterations and modificationswhich may differ particularly from those that have been described in thepreceding specification and description. It should be understood that wewish to embody within the scope of the patent warranted hereon all suchmodifications as reasonably and properly come within the scope of ourcontribution to the art.

1. An apparatus for ventilating a crankcase of a combustion engine,comprising: a ventilation duct extending from the crankcase to an intakesection of the combustion engine, at least one pressure drop causingoil-mist separator arranged along a length of said ventilation duct, acrankcase vacuum pressure regulating valve installed upstream ordownstream of said oil-mist separator which is adjustable dependent on apressure in the crankcase such that the pressure in the crankcase isprevented from falling below a lower pressure limit value, a relief ductextending from the crankcase to the intake section of the combustionengine, a crankcase excess pressure limiting valve arranged along alength of said relief duct, which excess pressure limiting valve can beadjusted to open upon detection of a predetermined pressure such that anupper pressure limit value is prevented from being exceeded in thecrankcase.
 2. An apparatus according to claim 1, wherein the crankcaseexcess pressure limiting valve is adjustable dependent on a differencebetween the crankcase pressure and a reference pressure.
 3. An apparatusaccording to claim 2, wherein atmospheric pressure is used as thereference pressure.
 4. An apparatus according to claim 1, wherein thecrankcase excess pressure limiting valve is a diaphragm valve with adiaphragm.
 5. An apparatus according to claim 4, wherein the diaphragminside the crankcase excess pressure limiting valve is fixed in adiaphragm chamber and subdivides said diaphragm chamber into a firstchamber section that communicates with atmospheric pressure and a secondchamber section that communicates with pressure in the crankcase.
 6. Anapparatus according to claim 5, wherein a beginning of that part of therelief duct that extends to the intake section is positioned in thecrankcase excess pressure limiting valve, wherein said beginning isformed as a valve seat that is directly cooperating with the diaphragmwhich serves as a portion of a valve body, the valve seat being arrangedin the second chamber section.
 7. An apparatus according to claim 6,wherein an effective area of the diaphragm is a multiple of across-sectional area of the valve seat.
 8. An apparatus according toclaim 1, wherein an additional duct bypassing the oil-mist separator isprovided, said bypass duct running from an inflow side to an outflowside of the oil-mist separator, with a separator differential pressurelimiting valve being arranged along a length of said bypass duct and,depending on a difference between an inflow side pressure and an outflowside pressure, being adjustable such that said differential pressurelimiting valve opens if a specifiable maximum pressure difference acrossthe oil-mist separator is exceeded.
 9. An apparatus according to claim1, wherein the ventilation duct and the relief duct are designed as acommon duct section over a part of their length.
 10. An apparatusaccording to claim 1, wherein the oil-mist separator, the crankcasevacuum pressure regulating valve, the crankcase pressure limiting valveand at least partial sections of the ducts are comprised to form asingle assembly-forming module that can be connected to the associatedcombustion engine either directly or via conduits.
 11. An apparatus forventilating a crankcase of a combustion engine, comprising: aventilation duct extending from the crankcase to an intake section ofthe combustion engine, at least one oil-mist separator positioned alonga length of said ventilation duct, a crankcase vacuum pressureregulating valve positioned along said length of said ventilation ductand arranged to prevent a pressure in the crankcase from falling below alower pressure limit value, a relief duct extending from the crankcaseto the intake section of the combustion engine, a crankcase excesspressure limiting valve arranged along a length of said relief duct, andarranged to prevent an upper pressure limit value from being exceeded inthe crankcase.
 12. An apparatus according to claim 11, wherein aflowpath extending through said relief duct and excess pressure limitingvalve includes at least one impingement surface for impingement bygasses flowing through said relief duct.
 13. An apparatus according toclaim 12, wherein said flowpath includes a sharp redirection of saidflowpath near a location of said impingement surface.
 14. An apparatusaccording to claim 11, wherein the crankcase excess pressure limitingvalve is adjustable dependent on a difference between the crankcasepressure and a reference pressure.
 15. An apparatus according to claim11, wherein said crankcase excess pressure limiting valve is a diaphragmvalve.
 16. An apparatus according to claim 11, wherein an additionalduct bypassing said oil-mist separator is provided, said bypass ductrunning from an inflow side to an outflow side of said oil-mistseparator, with a separator differential pressure limiting valve beingarranged along a length of said bypass duct and, depending on adifference between an inflow side pressure and an outflow side pressure,being adjustable such that said differential pressure limiting valveopens if a specifiable maximum pressure difference across said oil-mistseparator is exceeded.
 17. An apparatus according to claim 11, whereinsaid ventilation duct and said relief duct are designed as a common ductsection over a part of their length.
 18. An apparatus according to claim11, wherein said oil-mist separator, said crankcase vacuum pressureregulating valve, said crankcase pressure limiting valve and at leastpartial sections of said ducts are comprised to form a singleassembly-forming module that can be connected to the associatedcombustion engine either directly or via conduits.